Impact of Temperature and pH on the Survival of Listeria monocytogenes in Souse meat

by Kim, Mina K

Abstract (Summary)

Souse meat is an acidified, gelled product made with pork co-products such as ears, hearts, and tongues. This fully cooked, ready-to-eat (RTE) product is popular in the southern United States, and represents a significant volume of processed meat sold in this region. There is a ?zero-tolerance? policy for Listeria monocytogenes in RTE meat products. The growth/survival of L. monocytogenes in souse is unknown. The objective of this study was to determine the effectiveness of three different souse formulations in controlling the growth of L. monocytogenes at two different refrigerated storage temperatures. Three souse formulations (pH 4.3, 4.7, and 5.1) were produced in triplicate by a local processing plant. Products were subsequently surface-contaminated with a three-strain cocktail of L. monocytogenes. Uninoculated product served as the control. The initial contamination level was 105 cfu/cm2. Products were vacuum-sealed and stored at two different temperatures (5°C and 10°C). Microbial counts were monitored (total aerobic plate count and L. monocytogenes) twice weekly through 32 days storage. Data were analyzed by regression analysis and D values were compared using analysis of variance with means separation. Souse meat did not support the growth of L. monocytogenes, regardless of product formulation or storage temperature. D values for products with a pH of 4.7 or 5.1 were not different (40days at 5?C, TSAYE; 27 days at pH 4.7, 21 days at pH 5.1 at 5?C, TSAYE) (p>0.05). A lower product pH (4.3) decreased L. monocytogenes survival (D value = 9days) compared to higher pH products (p<0.05). D values for products stored at 5o C and 10o C did not differ (p>0.05). Consumer acceptability of pH 4.3 products was not different from (typical) pH 4.7 product (p>0.05). These results demonstrate that conventionally produced souse meat does not support the growth of L. monocytogenes and that inactivation of the organism is favored for products formulated at lower pH (<4.3).